The rise and fall of species on Earth might be driven in part by the undulating motions of our solar system as it travels through the disk of the Milky Way, scientists say.
Two years ago, scientists at the University of California, Berkeley found the marine fossil record shows that biodiversity—the number of different species alive on the planet—increases and decreases on a 62-million-year cycle. At least two of the Earths great mass extinctions—the Permian extinction 250 million years ago and the Ordovician extinction about 450 million years ago correspond with peaks of this cycle, which cant be explained by evolutionary theory.
Their idea hinges upon the fact that, appearances aside, stars are not fixed in space.
In particular, our Sun moves toward and away from the Milky Ways center, and also up and down through the galactic plane. One complete up-and-down cycle takes 64 million years— suspiciously similar to Earths biodiversity cycle.
The galactic bow shock is only present on the north side of the Milky Way’s galactic plane, because that is the side facing the Virgo Cluster as it moves through space, and it would cause superheated gas and cosmic rays to stream behind it, the researchers say. Normally, our galaxys magnetic field shields our solar system from this “galactic wind.” But every 64 million years, the solar systems cyclical travels take it above the galactic plane.
'When we emerge out of the disk, we have less protection, so we become exposed to many more cosmic rays,' Melott told SPACE.com.
The boost in cosmic ray exposure could have both a direct and indirect effect on Earths organisms, said KU paleontologist Bruce Lieberman. The radiation could lead to higher rates of genetic mutations in organisms or interfere with their ability to repair DNA damage, potentially leading to diseases like cancer.
'I think its a very nice idea,' said Philip Appleton, a Caltech astronomer. 'I think were only beginning to come to grips with these kinds of behaviors. We’re realizing that not only do galaxies interact with each other gravitationally, but also that the environment they re traveling through the 'wind' they create can actually produce noticeable effects.'
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